Frame antenna



Nov. 4, 1952 K. POSTHUMUS 2,617,033

FRAME ANTENNA Filed Jan. 16, 1948 KLAAS POJTHUMUA IN VEN TOR.

A 651V II Patented Nov. 4, 1952 FRAME ANTENNA Klaas Posthumus, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, 001111., as trustee Application January 16, 1948, Serial No. 2,774 In the Netherlands January 25, 1947 12 Claims. 1

this invention relates to a frame aerial for transmitting and/or receiving purposes and consists in that, in order to increase the radiation resistance of the frame aerial, one or more shortcircuit turns are provided which are inductively coupled with the frame aerial coil and extend outwards from the periphery of the coil.

Preferably, the short-circuit turns jointly constitute an annularsurface surrounding the coil body, and the short-circuit turns may embrace ring sectors adjoining each other.

In using the invention it is achieved, in addition to other advantages referred to hereinafter, that the effective surface of the frame-aerial coil and consequently the radiation resistance of the aerial are increased without modification of the coil, since the short-circuit turns, operating as transformers, fundamentally urge the current in the frame-aerial coil towards the outer periphery of the short-circuit turns.

Particularly in the case of frame aerials, in which the frame-aerial coil should only consist of a single turn having a small surface (short length of the turn) in order to obivate interfering natural frequencies of the frame aerial, the use of a plurality of sector-shaped short-circuit turns according to the invention ofiers considerable advantages.

If with a give size of the annular surface occupied by the short-circuit turns, the peripheral length of each of the short-circuit turns is reduced by increasing number of them, interfering natural frequencies of the short-circuit turns may be largely obviated, so that the frame-aerial according to the invention is particularly suitable for the transmission of wide frequency bands with horizontal polarisation as is often neces sary, for instance in television, multiplex telephany and radio navigation.

In order that the invention and its advantages may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawings in which the figures represent, by way of example, several embodiments thereof.

Fig. 1 is a plan view of a frame-aerial comprising a single short-circuit turn and Fig. 2 is the experimentally determined polar radiation diagram.

Figs. 3 and 4 are a plan View and a sectional view respectively of a frame-aerial comprising a plurality of sector-shaped short-circuit turns,

Fig. 5 being the corresponding radiation diagram.

Fig. 6 illustrates, by way of example, one form of a frame aerial according to the invention comprising particularly formed short-circuit turns, and Fig. 7 is a sectional detail view of a particular form of a frame-aerial coil Fig. 8 illustrating another executional example.

In Fig. 1 the reference numeral I designates a frame-aerial coil which consists of a single short-circuit turn and is connected to a transmission lead extending in accordance with the axis of the coil, According to the invention the coil I is surrounded by an annular metal plate 3 which is located in the coil plane and exhibits a radially directed interruption 4. In conjunction with skin effects the said plate may be imagined to be replaced by one short-circuit turn extending in accordance with the periphery of the plate.

A current occurring in the frame coil induces on the short-circuit turn a current proportional thereto which, provided that the electrical length of the short-circuit turn is smaller than half the operating wavelength, is equally directed throughout the outer periphery of the short-circuit turn. The circuit current thus produced comprises. however, a larger efiective surface than the coil I.

In order to explain this effect reference ma be made to the analogy existing between the present frame aerial used for receiving purposes and the short-circuit turn which, in the case of inductive high-frequency heating of a work piece, is often arranged between this workpiece and the surrounding inductances coil and is usually called concentrator. In both cases the magnetic field of lines of force is concentrated in the frame coil I or the work piece, which may be interpreted as an increase in effective surface and in radiation resistance of the frame aerial or the work piece. The same effect occurs, of course, in the use of the frame aerial according to the invention for transmitting purposes.

In an experimental form of the'frameaerial shown in Fig. 1 the external diameter of the short-circuit ring 3 was chosen to be ,4; of the operating wavelength (approximately 68 cms.) with a diameter of the coil I of approximately of the wavelength.

Owing to the comparatively great length of the outer periphery of the short-circuit turn the current occurring in situ is not equally directed everywhere and this results in a radiation diagram exhibiting outstanding loops as shown in Fig. 2.

However, in the case of constant peripheral dimensions this can be avoided by a sector-wise subdivision of the short-circuit ring 3. Figsp3 and 4 show a modified form of construction comprising eight sector-shaped short-circuit turns 6, whereas Fig. shows the corresponding radiation diagram. The substantially circular radiation diagram (maximum divergence 5%) proves that in this event the current along the outer periphery of the short-circuit sectors is everywhere equally directed. Currents occurring in neighbouring sector edges are oppositely directed, even if current loops and nodes occur along these edges, and do not contribute to the radiation. Consequently, the current in coil I is fundamentally urged towards the outer periphery of the system by the short-circuit turns.

In the frame-aerial consisting of a single turn the peripheral length of this turn is a measure of the frequency-dependency of the system; in the present case, however, it is not the length of the outer periphery of the system but the size of the short-circuit turns which is a measure of the frequency-dependency of the system.

.A further reduction in length of the short-circuit turns can be obtained by radial subdivision of the annular surface occupied by the shortcircuit turns, for example in the manner illustrated in Fig. 8, where the inner ring comprises four short-circuit turns and the outer ring eight short-circuit turns 9 and I0 respectively having substantially equal relative peripheral lengths. Thus a particularly great peripheral length of the system is ensured with a constant current along the outer periphery.

If the electric length of the short-circuit turns is approximately V4 /1}, and so forth) of the operating wavelength, the short-circuit turns behave as impedance transformers, which may be v utilised, for example for attaining a very high input impedance of coil I; however, this involves an outstanding frequency-dependency of the system.

For the transmission of wide frequency ranges the said electric lengths of the short-circuit turns should be avoided, but it is also possible to reduce the frequency-dependency by giving successive short-circuit turns electric lengths which diverge on different sides from one fourth of the operating wavelength (for example by 5%). This may, for example, be achieved either by a suitable choice of the radial lengths of the sectors 6 or of the opening angles of the sectors or by combination of these two measures.

i d Fig. 6 1s a sectional view of one form of a frame-aerial according to the invention, in which the surface occupied by the short-circuit turns 6' is conical. Operation and effect of the shortcircuit turns are not affected by such a shape,,--;

which is of importance for structural reasons.

A satisfactory operation of the system requires a very close coupling between the short-circuit turns 6 and the coupling coil 1; for this purpose neighboring edges of the surface of the framecoil and the annular surface occupied by the short-circuit turns may be constructed to overlap one another.

In Fig. 7 one form of the frame-aerial suitable for this purpose is shown in a sectional de--- tail view of Fig. 3. The turn of the coil l exhibiting a U-shaped section 1 includes the inner edge 8 of the short-circuit sectors 6.

In order to reduce the stray-radiation occurring due to the radial interruptions in the annular surface occupied by the short-circuit turns, neighbouring edges of the surface of the frame structed to overlap one another with the interposition :of insulating material.

.For the short-circuit turns use should, of

4 course, be made of metal having a low specific resistance, in order to avoid undue losses. If desired, the sectors at the primarily current-conveying areas may be coated, for instance by cataphoresis, with a thin metal layer of high conductivity.

To obviate as much as possible the detrimental influence of high current densities, short-circuit turns consisting of not too thin metal plates (for example of some few mms.) have proved to be suitable.

The sectors 6 and the coil 1 may be mounted on a plate of insulating material. For the sake of clearness the mechanical supporting means are not shown in the drawing.

If desired, the conductive parts of the aerial system according to the invention may consist of metal coatings applied, for example, by chemical agency, on to insulating material.

The sectors may be supported at the centre by metal parts which may be interconnected, if desired.

What I claim is:

l. A frame aerial structure comprising a centrally disposed open-circuited coil, and a plurality of short-circuited loops inductively coupled to said coil and circumferentially arranged thereabout, the loops extending outwardly from the periphery from the coil and being shaped to define adjoining and electrically separated sectors in the area encircling said coil.

2. A high-frequency frame aerial structure comprising a centrally disposed open-circuited coil, and a plurality of short-circuited loops inductively coupled to said coil and circumferentially arranged thereabout, the loops extending outwardly from the periphery from the coil and being shaped to define adjoining electrically separated sectors in an annular surface surrounding said coil.

3. An arrangement, as set forth in claim 2, wherein said loops are constituted by metallic plates which with respect to high-frequency currents have an effect equivalent to that of short- 5 circuited loops.

4. An arrangement, as set forth in claim 2, wherein the outer circumference of the central coil is smaller than the operating wavelength of the aerial structure and the outer circumference 0 of the annular surface occupied by said loops is larger than said operating wavelength.

5. A high-frequency frame aerial structure comprising a centrally disposed open-circuited single-turn coil, and a plurality of short-circuited loops inductively coupled to said coil and circumferentially arranged thereabout, the loops extending outwardly from the periphery from the coil and being shaped to define adjoining electrically separated sectors in an annular surface surrounding said coil.

6. An arrangement, as set forth in claim 5, further characterized by the fact that the shortcircuited loops differ in electrical length.

7. An arrangement, as set forth in claim 5, wherein adjacent edges of said sector-shaped loops are disposed in overlapping relation.

8. An arrangement, as set forth in claim 5, wherein said single-turn coil has a U-shaped cross section to define a circular channel, the edges of said loops adjacent said coil being received within said channel to effect inductive coupling between saidloops and said coil.

9. A frame aerial structure comprising a centrally disposed open-circuited coil, and a plurality of short-circuited loops inductively coupled to said coil and circumferentially arranged thereabout, the loops extending outwardly from the periphery of said coil and being shaped to define adjoining sectors in a conical surface surrounding said coil.

10. A frame aerial structure comprising a centrally disposed open-circuited single-turn coil, and a plurality of short-circuited loops constituted by metallic plates inductively coupled to said coil and circumferentially arranged thereabout, the loops extending outwardly from the periphery of said coil and being shaped to define adjoining sectors in a conical surface surrounding said coil, adjacent edges of said loops being disposed in overlapping relation.

11. A frame aerial structure comprising a centrally disposed open-circuited coil, a first series of short-circuited loops inductively coupled to said coil and circumferentially arranged thereabout, the loops in said first series extending outwardly from the periphery of said'coil and being shaped to define adjoining sectors in an annular surface surrounding said coil, and a second series of short-circuited loops circumferentially arranged about said first series of loops and inductively coupled thereto, the loops in said second series extending outwardly and being shaped to define adjoining sectors in an an- 6 nular surface surrounding the annular surface occupied by said first series.

12. An arrangement, as set forth in claim 10, wherein the number of short-circuited loops in the second series is greater than the number in the first series.

KLAAS POSTHUMUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

